The present invention relates to a device for carrying an object thereon, such as a pan head on which a broadcasting television (TV) camera, for example, is placed, and more particularly, to a tiltable-type object carrying device permitting a TV camera placed thereon to be swiveled and tilted for shooting a scene.
In pan heads of this type in general, when an object placed thereon is inclined, or tilted, with respect to an axis of horizontal rotation, the center of gravity of the object lowers and thus, in some cases, the object falls down. To prevent this, a technique is employed, as disclosed in Examined Japanese Patent Publication (KOKOKU) No. 2-27560, for example, in which a spring balancing with the weight of the object is used. However, this technique is generally applicable only to the case where a lightweight object such as a small-sized video camera is placed on the pan head, though the bearable weight varies depending on the spring capacity.
In the case of supporting a heavy object such as a large-sized camera equipped with a long focal-distance lens system, a pan head called cam head is often used. Such a cam head includes a cam and a cam follower, as disclosed in British Patent No. 1,316,250 and Examined Japanese Patent Publication No. 2-35198, for example, and as an object placed on the cam head is tilted, the center of gravity thereof shifts horizontally such that the potential energy remains the same.
Apart from these types of cam head, Examined Japanese Patent Publication No. 64-10719 discloses an object carrying device with a different structure utilizing a Reuleaux mechanism known in the art, wherein a pair of sliding rods arranged in an inverted-V form are rotatably attached to opposite sides of a supporting base for carrying an object thereon and are moved along guide rollers when the object is to be tilted. Also, the publication of WO92/09846 discloses a device using a combination of special link mechanisms. In both of these devices, as an object placed thereon is tilted, the center of gravity thereof shifts horizontally.
The cam heads mentioned above are associated with a problem that the cam needs to be replaced with one having a different shape in accordance with the height of the center of gravity of an object to be placed on the cam head. Accordingly, each time the height of the center of gravity changes due to replacement of cameras or lenses, the cam must be replaced with a suitable one, and this makes the preparatory work for shooting complicated.
On the other hand, the technique disclosed in Examined Japanese Patent Publication No. 64-10719 and that described in the publication of WO92/09846 can cope with change in the height of the center of gravity of the object, without requiring complicated adjustment such as replacement of cams.
However, according to the technique disclosed in Examined Japanese Patent Publication No. 64-10719, in order to obtain a large tilt angle, it is necessary that extremely long sliding rods should be used. The technique described in the publication of WO92/09846, on the other hand, requires a complicated link mechanism, and accordingly, the sliding rods or links need to have high rigidity. If the sliding rods or links are made of a commonly used material or have ordinary dimensions, they will possibly be deflected or fractured.
The present invention was created to solve the above problems, and an object thereof is to provide a tiltable-type object carrying device which enables the center of gravity of an object placed thereon to shift horizontally with tilting of the object and which also requires only a simple operation to cope with change in the height of the center of gravity of the object.
According to the present invention, there is provided a tiltable device for carrying an object thereon, comprising: a base; first and second rails arranged on the base and inclined such that the first and second rails are located close to each other at one end and remote from each other at other end; a first lateral link having opposite ends movably arranged on the first and second rails, respectively; a second lateral link parallel to the first lateral link and serving as a tiltable base for carrying an object thereon; and first and second vertical links parallel to each other and each rotatably connected to the first and second lateral links for holding the first and second lateral links together.
Preferably, an orientation control section is provided for maintaining vertical orientation of the first and second vertical links. The orientation control section includes a horizontal portion horizontally movable relative to the base, a vertical portion extending vertically from the horizontal portion, and holding means permitting one of the first vertical link, the second vertical link and a third vertical link connected to the first and second lateral links to be vertically movably held by the vertical portion. Alternatively, the orientation control section includes a supporting member arranged on the base, and a pair of lateral links rotatably supported at one end by the supporting member and rotatably supported at other end by one of the first vertical link, the second vertical link and a third vertical link connected to the first and second lateral links, wherein the supporting member, the pair of lateral links, and the above one of the first vertical link, the second vertical link and the third vertical link connected to the first and second lateral links constitute a parallelogrammic link.
Further preferably, adjusting means is provided which is coupled to the first and second rails for adjusting an angle of inclination thereof. The adjusting means includes first and second nuts coupled to the first and second rails, respectively, and a threaded rod having a first threaded portion on which the first nut is fitted, and a second threaded portion on which the second nut is fitted and which has a thread cut in a different direction from that of the first threaded portion.